Lepton Universality Violation by Kaluza-Klein Neutrinos in $b\to s l l$ transition

TL;DR

This paper proposes that Kaluza-Klein modes of a singlet Dirac neutrino in large extra dimensions can naturally explain the observed lepton universality violation in $b o s l l$ decays, aligning with recent experimental anomalies.

Contribution

It introduces a model where KK neutrino modes account for the $C_9^{bs l l}=-C_{10}^{bs l l}$ anomaly, linking extra dimensions to flavor physics deviations.

Findings

KK modes induce the required Wilson coefficient pattern.

Fundamental scale can be as low as 2.9 TeV with two extra dimensions.

Model explains the $R_K$ anomaly without new particles at current collider energies.

Abstract

Recent measure of $R_K$, involving the decays of $b\to s l^+ l^-$, by the LHCb at CERN strengthened the deviation from the Standard Model prediction. The best fit in the updated global analysis suggests that the muon specific Wilson coefficients $C^{bs\mu \mu}_9=-C^{bs\mu \mu}_{10}$ should be about $-0.41$. In this paper, we show that the accumulate effects of KK modes of a singlet Dirac neutrino propagating in the large extra-dimensional space naturally provide $C^{bs l l}_9=-C^{bs l l}_{10}$ to explain the anomaly. By taking the muon Yukawa coupling to be of ${\cal O}(1)$, the fundamental scale in the extra-dimensional framework should be lowered down to about $2.9$ TeV if there are two additional spatial dimensions.